X-linked agammaglobulinaemia (XLA) is caused by mutation of the BTK gene. Early immunological screening is important in children with recurrent infection to avoid delay in diagnosis and treatment. A 9-year-old boy with delayed XLA diagnosis presented with a history of recurrent sinopulmonary infection since the age of 1 year old. He had a severe Achromobacter xylosoxidans bacteraemia at the age of 8 years that was successfully treated with intravenous antibiotics. Further immunological screening and genetic testing confirmed the diagnosis of XLA and he was treated with intravenous immunoglobulin replacement therapy. This case provides a valuable information on the diagnosis, treatment and management of XLA, emphasising the importance of early immunological investigations to avoid diagnostic delay.